[CACHE][TAG] Use downloads and sstate-cache on tag

* In a first implementation of the build logic, the downloads and
sstate-cache were supposed to be used only on sheduled and MR builds.
However, as the number of supported boards increase, there is more necessity of
CPU and time to get all Yocto images built when a tag is performed. For
this reason we decide to remove the differentiation at least as long as
the build server is not upgraded.